The present invention relates to a heater drive circuit and, more particularly, to one suitable for use with, for example, an ink jet printer for driving a heater which is adapted to control the temperature of ink.
An ink jet printer generally employs a heater for controlling the temperature of ink ejected from a head to a predetermined appropriate level. A prior art circuit for driving the heater comprises a sensor responsive to a temperature of the heater, an error amplifier having an inverting input supplied with an output of the sensor and a non-inverting input selectively supplied with a relatively high reference voltage which is applied to the heater at the time of buildup or startup of the heater and a reference voltage applied to the heater to maintain ink at the appropriate temperature, and an output transistor having a base supplied with an output voltage of the error amplifier, a collector connecting to a power source and an emitter connecting to the heater.
In the heater drive circuit having the above construction, little heat is generated at a buildup of the heater because the output transistor consumes only small power at the buildup stage. However, while the heater is under a stationary or normal operating condition for maintaining the appropriate ink temperature, the collector loss at the transistor is large so that substantial heat is generated to increase the power consumption. This requires provision of a heat sink and, therefore, an additional space for accommodating it, resulting in a bulky and expensive construction as a whole.